Mouse growth hormone secretagogue receptor

ABSTRACT

A mouse growth hormone secretagogue receptor has been isolated, cloned and sequenced. This receptor is characteristic of the G-protein family of receptors. Mouse growth hormone secretagogue receptors may be used to screen and identify compoumds which bind to the mouse growth hormone secretagogue receptor. Such compounds may be used in the treatment of conditions which occur when there is a shortage of growth hormone, such as observed in growth hormone deficient children, elderly patients with musculoskeletal impairment and those recovering from hip fracture and osteoporosis. Targeted disruption of the mouse GHS-R gene may prove useful in elucidation of the mechanism of action and role of the growth hormone secretagogues in human and animal physiology.

This Application is a 371 of PCT/US99/153751 filed on Jul. 8, 1999, which claims benefit of U.S. Provisional Application No. 60/092,361 filed on Jul. 10, 1998.

FIELD OF THE INVENTION

This invention relates to a newly identified receptor, the mouse growth hormone secretagogue receptor (mGHS-R), nucleic acids encoding this receptor; and to the use of a mGHS-R to identify growth hormone secretagogues and compounds that modulate mGHS-R function.

BACKGROUND OF THE INVENTION

Growth hormone secretagogues (GHSs) and secretagogue-like compounds, both peptide and non-peptide, bind to and exert their biological effects (i.e., release of growth hormone (GH)) through a G protein-coupled receptor (GPC-R) distinct from the receptors for growth hormone releasing hormone (GHRH) and somatostatin (SST) (Pong et al., 1996 Mol. Endocrin. 10:57-61). The molecular cloning of this growth hormone secretagogue receptor (GHS-R) capitalized on the pivotal observation that GHSs transduce their signal through activation of the phospholipase C pathway (Cheng et al., 1991 Endocrinology 129:3337-3342; Howard et al., 1996 Science 273:974-977). cDNA and genomic DNA cloning from human, swine, and rat showed that the GHS-R is a protein of 364/366 amino acids containing 7 putative alpha-helical transmembrane (TM) domains, a signature feature of GPC-Rs (Howard et al. 1996; McKee et al., 1997 Mol. Endocrin. 11:415-423). In all species evaluated, the GHS-R is encoded by a single highly-conserved gene containing one intron, placed at the C-terminal end of TM domain 5.

The biology of the growth hormone secretagogues (GHSs) is still in a relatively early stage of development. Research is focused on identification of the GHS natural ligand system and understanding the role of the GHS-R in brain regions (substantia nigra, dentate gyrus, hippocampus) other than those traditionally thought to be involved in GH secretion (Bennett et al. 1997; Guan et al. 1997).

It would be desirable to know the molecular structure of growth hormone secretagogue receptors in order to analyze this new receptor family and understand its normal physiological role in: concert with the actions of GHRH and somatostatin. This could lead to a better understanding of the in vivo processes which occur upon ligand-receptor binding. Further, it would be desirable to use cloned-growth hormone secretagogue receptors as essential components of an assay system which can identify new growth hormone secretagogues which would confer a significant benefit on children and adults deficient in growth hormone, the frail elderly, those in post-hip fracture rehabilitation and post-operative recovery patients.

SUMMARY OF THE INVENTION

This invention relates to a novel receptor, mouse growth hormone secretagogue receptor (mGHS-R), which is free from receptor associated proteins. A further aspect of this invention is mGHS-R which is isolated or purified.

Another aspect of this invention is mGHS-Rs which are encoded by substantially the same nucleic acid sequence, but which have undergone changes in splicing or other RNA processing-derived modifications or mutagenesis induced changes, so that the expressed protein has a homologous, but different amino acid sequence from the native form. These variant forms may have different and/or additional functions in animal physiology or in vitro in cell based assays.

Growth hormone secretagogue receptors are proteins containing various functional domains, including one or more domains which anchor the receptor in the cell membrane, and at least one ligand binding domain. As with many receptor proteins, it is possible to modify many of the amino acids, particularly those which are not found in the ligand binding domain, and still retain at least a percentage of the biological activity of the original receptor. Thus, this invention specifically includes modified functionally equivalent mGHS-Rs which have deleted, truncated, or mutated N-terminal portions. This invention also specifically includes modified functionally equivalent mGHS-Rs which contain modified and/or deletions in other domains, which are not accompanied by a loss of functional activity.

Additionally, it is possible to modify other functional domains such as those that interact with second messenger effector systems, by altering binding specificity and/or selectivity. Such functionally equivalent mutant receptors are also within the scope of this invention.

A further aspect of this invention are nucleic acids which encode a mouse growth hormone secretagogue receptor or a functional equivalent. These nucleic acids may be free from associated nucleic acids, or they may be isolated or purified. For most cloning purposes, cDNA is a preferred nucleic acid, but this invention specifically includes other forms of DNA as well as RNAs which encode a mGHS-R or a functional equivalent.

Yet another aspect of this invention relates to vectors which comprise nucleic acids encoding mGHS-R or a functional equivalent. These vectors may be comprised of DNA or RNA; for most cloning purposes DNA vectors are preferred. Typical vectors include plasmids, modified viruses, bacteriophage and cosmids, yeast artificial chromosomes, transposable elements and other forms of episomal or integrated DNA that can encode a mGHS-R. It is well within the skill of the ordinary artisan to determine an appropriate vector for a particular gene transfer or other use.

A further aspect of this invention are host cells which are transformed with a vector comprising a gene which encodes a mouse growth hormone secretagogue receptor or a functional equivalent. The host cell may or may not naturally express a GHS-R on the cell membrane. Preferably, once transformed, the host cells are able to express the mouse growth hormone secretagogue receptor or a functional equivalent on the cell membrane. Depending on the host cell, it may be desirable to adapt the DNA so that particular codons are used in order to optimize expression. Such adaptations are known in the art, and these nucleic acids are also included within the scope of this invention. Generally, mammalian cell lines, such as COS, HEK-293, CHO, HeLa, NS/0, CV-1, GC, GH3 or VERO cells are preferred host cells, but other cells and cell lines such as Xenopus oocytes or insect cells, may also be used.

Another aspect of this invention is a process for identifying nucleic acids encoding mouse growth hormone secretagogue related receptors comprising hybridizing a first nucleic acid encoding a mouse growth hormone secretagogue receptor with a second nucleic acid suspected of comprising nucleic acids encoding a growth hormone secretagogue receptor, wherein the hybridizing takes place under relaxed or moderate post hybridizational washing conditions; and identify areas of the second nucleic acid where hybridization occurred.

BRIEF DESCRIPTION OF THE FIGURES

FIGS 1A-1B is the DNA sequence encoding the mouse GHS-R, 5′ and 3′ flanking regions and the intron; SEQ ID NO:1.

FIG. 2 is the DNA sequence encoding the open reading frame (ORF) of the mouse GHS-R; SEQ ID NO:2.

FIGS. 3A-3B is the deduced amino acid sequence of the mouse GHS-R; SEQ ID NO:3.

FIGS. 4A-4B is an amino acid alignment of the mouse GHS-R with other GHS-R's from several species (human—SEQ ID NO:4, rat—SEQ ID NO: 5, and swine—SEQ ID NO:6).

DETAILED DESCRIPTION OF THE INVENTION

As used throughout the specification and claims, the following definitions shall apply:

Growth Hormone Secretagogue—any compound or agent that directly or indirectly stimulates or increases the release of growth hormone in an animal.

Ligands—any molecule which binds to the mGHS-R of this invention. These ligands can have either agonist, partial agonist, partial antagonist or antagonist activity.

Free from receptor-associated proteins—the receptor protein is not in a mixture or solution with other membrane receptor proteins.

Free from associated nucleic acids—the nucleic acid is not covalently linked to DNA which it is naturally covalently linked in the organism's chromosome.

Isolated receptor—the protein is not in a mixture or solution with any other proteins.

Isolated nucleic acid—the nucleic acid is not in a mixture or solution with any other nucleic acid.

Functional equivalent—a receptor which does not have the exact same amino acid sequence of a naturally occurring mouse growth hormone secretagogue receptor due to alternative splicing, deletions, mutations, or additions, but retains at least 1%, preferably 10%, and more preferably 25% of the biological activity of the naturally occurring receptor. Such derivatives will have a significant homology with a natural mGHS-R and can be detected by reduced stringency hybridization with a DNA sequence obtained from a mGHS-R. The nucleic acid encoding a functional equivalent has at least about 50% homology at the nucleotide level to a naturally occurring receptor nucleic acid.

Purified receptor—the receptor is at least about 95% pure.

Purified nucleic acid—the nucleic acid is at least about 95% pure.

Standard or high stringency post hybridizational washing conditions—6×SSC at 55° C.

Moderate post hybridizational washing conditions—6×SSC at 45° C.

Relaxed post hybridizational washing conditions—6×SSC at 30° C.

The mouse isoform of the previously identified GHS-R was cloned from two genomic DNA libraries for the generation of a GHS-R knock-out mouse. This isoform has been shown to be functionally activated by secretagogues such as growth hormone releasing peptide GHRP-6 and MK-0677 through expression studies of the complete and contiguous open reading frame of mGHS-R using the aequorin biolumenescence assay. The proteins of this invention were found to have structural features which are typical of the 7-transmembrane domain (TM)-containing G-protein linked receptor superfamily (GPC-R's or 7-TM receptors), including seven transmembrane regions, three intra- and extracellular loops, and the GPC-R protein signature sequence. Thus, mGHS-R, as an additional member of the growth hormone secretagogue family of receptors, constitutes a new member of the GPC-R family of receptors. Note not all regions are required for functioning, and therefore this invention also comprises functional receptors which lack one or more non-essential domains.

Sequence analysis of the mGHS-R revealed, further, the presence of a non-coding, intronic sequence at nt 790 corresponding to a splice-donor site (G/GT) (FIG. 1). This sequence insertion occurs two amino acids after the completion of the predicted transmembrane domain (TM) 5 (leucine-263), thus dividing the ORF of the mouse GHS-R into an amino-terminal segment (encompassing the extracellular domain, TM-1 through TM-5, and the first two intra-and extra-cellular loops) and a carboxyl-terminal segment containing TM-6, TM-7, the third intra- and extra-cellular loops, and the intracellular domain. The point of insertion and flanking DNA sequence are highly conserved between human, swine, rat and mouse. Comparison of the complete ORF encoding the murine GHS-R type Ia protein sequence (FIG. 4) to rat, human and swine GHS-R homologs reveals a high degree of sequence identity (mouse vs. rat, 99.5%; mouse vs. human 95%; mouse vs. swine 94%).

The mGHS-Rs of this invention also share some sequence homology with previously cloned GPC-receptors including the rat and human neurotensin receptor (approximately 32% identity) and the rat and human thyrotropin releasing hormone (TRH) receptor (approximately 29% identity).

The mGHS-R and fragments are immunogenic. Thus, another aspect of this invention is antibodies and antibody fragments which can bind to mGHS-R or a mGHS-R fragment. These antibodies may be monoclonal antibodies and produced using either hybridoma technology or recombinant methods. They may be used as part of assay systems or to deduce the function of a mGHS-R present on a cell membrane.

A further aspect of this invention are antisense oligonucleotides—nucleotides which can bind to mGHS-R nucleotides and modulate receptor function or expression.

A further aspect of this invention is a method of increasing the amount of mGHS-Rs on a cell membrane comprising, introducing into the cell a nucleic acid encoding a mGHS-R, and allowing expression of the mGHS-R.

A mGHS receptor, preferably immobilized on a solid support, may be used diagnostically for the determination of the concentration of growth hormone secretagogues, or metabolites thereof, in physiological fluids, e.g. body fluids, including serum, and tissue extracts, as for example in patients who are undergoing therapy with a growth hormone secretagogue.

The administration of a mGHS receptor to a patient may also be employed for purposes of amplifying the net effect of a growth hormone secretagogue by providing increased downstream signaling following administration of the growth hormone secretagogue thereby diminishing the required dosage of growth hormone secretagogue; or diminishing the effect of an overdosage of a growth hormone secretagogue during therapy.

Yet a further aspect of the present invention is a method of identifying ligands comprising contacting the mGHS-R with a compound suspected of being a ligand specific for said receptor and determining whether binding occurs, binding constituting a positive indication of the presence of a ligand.

Ligands detected using assays described herein may be used in the treatment of conditions which occur when there is a shortage of growth hormone, such as observed in growth hormone deficient children, elderly patients with musculoskeletal impairment and those recovering from hip fracture, and osteoporosis.

Targeted disruption of the mouse GHS-R gene may also prove useful in elucidation of the mechanism of action and role of the growth hormone secretagogues in human and animal physiology.

The following, non-limiting Examples are presented to better illustrate the invention.

EXAMPLE 1

Isolation of Mouse GHS-R

A mouse (strain 129, liver) genotic library constructed in the vector lamda Fix II (Stratagene) was screened under moderate stringency hybridization conditions with a complete ORF probe derived from the swine GHS-R. Nylon filters repesenting 1.2×10⁶ PFU were hybridized overnight at 58° C. in 6×SSC containing 10% dextran sulfate, 2% SDS, 0.5 M NaCl, and 100 μg/ml salmon sperm DNA with the random prime ³²P-labeled swine GHS-R probe. Filters were washed in 4×SSC, 1% SDS at room temerature for 20 minutes, 4×SSC, 1% SDS at 55° C. for 30 min, 2×SSC, 1% SDS at 55° C. for 30 min, and 2×SSC, 1% SDS at 62° C. for 30 min. Three positive clones were identified, phage DNA was isolated, and partial DNA sequencing performed to verify that they encoded the murine GHS-R gene. In addition, a mouse genomic library constructed in a BAC vector and gridded in a filter array (Genome Systems, Inc) was screened under moderate stringency hybridization conditions as given above with a complete ORF probe dervived from the human GHS-R. A positive clone was identified from the BAC library.

EXAMPLE 2

Sequencing of Mouse GHS-R

The BAC clone was sequenced with ABI Prism BigDye terminator cycle sequencing ready reaction mix (P/N 4303149; PE Applied Biosystems, Foster City, Calif.) using 1 μg DNA/reaction, 5% DMSO, 100 ng primer—standard cycle sequencing. Reactions were run on an ABI Prism 377 DNA Sequencer with XL Upgrade (ABI Prism 377XL).

DNA from the positive lambda clones was prepared from a liquid lysate of the E. coli strain XLBlue MRA minus. For DNA sequencing, 500 ng of DNA was used under the same conditions as given above.

EXAMPLE 3

Analysis of Mouse GHS-R Sequence

Sequence analysis revealed the presence of a non-coding, intronic sequence at nt 790 corresponding to a splice-donor site (G/GT) (FIG. 1). This sequence insertion occurs two amino acids after the completion of the predicted transmembrane domain (TM) 5 (leucine-263), thus dividing the ORF of the mouse GHS-R into an amino-terminal segment (encompassing the extracellular domain, TM-1 through TM-5, and the first two intra-and- extra-cellular loops) and a carboxyl-terminal segment containing TM-6, TM-7, the third intra- and extra-cellular loops, and the intracellular domain. The point of insertion and flanking DNA sequence are highly conserved between human, swine, rat and:mouse. Comparison of the complete ORF encoding the murine GHS-R type Ia protein sequence (FIG. 4) to rat, human and swine GHS-R homologs reveals a high degree of sequence identity (mouse vs. rat, 99.5%; mouse vs. human 95%; mouse vs. swine 94%).

EXAMPLE 4

Construction of Mouse GHS-R Expression Plasmid

For expression studies in mammalian cells, a contiguous ORF (FIGS. 2 and 3) was assembled in the vector pcDNA-3 (Invitrogen) by overlapping PCR to remove the single intron present following nucleotide 790 of the ORF. To subclone, the Advantage HF PCR kit (K 1909-1; Clonetech Laboratories, Inc, Palo Alto, Calif.) was used under the following conditions: 94° C. for 1 min;, then 25 cycles of the following: 94° C. for 15 sec, 55° C. for 15 sec, and 68° C. for 3 min. The primers used were: primer 1-5′GGG CCC GAA TTC GCC GCC ATG TGG AAC GCG ACG CCC AGC 3′ (SEQ ID NO:7, including EcoR I site, Kozak initation sequence, and translational start Met); primer 2-5′CAC CAC CAC AG C AAG CAT CTT CAC TGT CTG3′ (SEQ ID NO:8; nucleotides shown in italic type overlap exon 2); primer 3-5′AAG ATG CTT G CT GTG GTG GTG TTT GCT TTC ATC3′ (SEQ ID NO:9; nucleotides shown in italic type overlap exon 1); and primer 4-5′AGT TTA GCG GCC GCT CAT GTA TTG ATG CTC GAC TTT GT3′ (SEQ ID NO:10, including Not I site and stop codon). “Overlapping” PCR was performed. The first PCR reactions were performed with primers 1 and 2 (exon 1) or 3 and 4 (exon 2). The second PCR reactions were performed with primers 1 and 4 (ORF). The second product was digested with EcoRI and NotI, agarose gel purified, ethanol precipitated, phenol extracted, and ligated into pcDNA3 with Ready-to-Go T4 Ligase (27-0361-01; Pharmacia, Piscataway, N.J.), and transformed into SCS1 cells (200231; Stratagene, La Jolla, Calif.). DNA was isolated with Wizard Plus miniprep (A1460; Promega, Madison, Wis.) and 500 ng was sequenced as above, but without DMSO.

EXAMPLE 5

Functional Activity of Mouse GHS-R

Measurement of mouse GHS-R expression in the aequorin-expressing stable reporter cell line 293-AEQ17 (Button et al., 1993 Cell Calcium 14:663-671.) was performed using a Luminoskan RT luminometer (Labsystems Inc., Gaithersburg, Md. 293-AEQ17 cells (8×10⁵ cells plated 18 hr. before transfection in a T75 flask) were transfected with 22 μg of pcDNA-3/mouse GHS-R plasmid DNA and 264 μg lipofectamine (Life Technologies). Forty hours after transfection, the apo-aequorin in the cells was charged for 1 hour with coelenterazine CP (10 μM) under reducing conditions (300 mM reduced glutathione) in ECB buffer (140 mM NaCl, 20 mM KCl, 20 mM HEPES-NaOH, pH=7.4, 5 mM glucose, 1 mM MgCl₂, 1 mM CaCl₂, 0.1 mg/ml bovine serum albumin). The cells were harvested, washed once in ECB medium and resuspended to 500,000 cells/ml. One hundred (100) μg of cell suspension (corresponding to 5×10⁴ cells) was then injected into each well of a 96-well microtiter test plate, and the integrated light emission was recorded over 30 seconds, in 0.5 second units. Twenty (20) μl of lysis buffer (0.1% final Triton X-100 concentration) was then injected and the integrated light emission recorded over 10 seconds, in 0.5 second units. The “fractional response” values for each well were calculated by taking the ratio of the integrated response to the initial challenge to the total integrated luminescence including the Triton X-100 lysis response. Data were analyzed using GraphPad Prism software V.2.0 (GraphPad Software, San Diego, Calif.).

10 1 4009 DNA Mus musculus 1 agagaggagc cctcacacac tcgctttgca gcgcctgcct tccgcaagag cccacgcact 60 cggacgcttg tggggagcac gacaggcttg ctggggcgag atctccagtg ccaggcaact 120 gctggtggcg ccgccgtttg agtgacaggt aagtgagtgc gtgacagtcg aggctgtatt 180 gggagaccgg gactgtgtgg ggaagatagt gggaaggggg aagaaaagag agatgtggga 240 gggaggggag aggaggaacg gaaggaaata gggagagacg tgcagtgggt cactctcttc 300 ctttcatcgc taatgttcgc acccccattc caccttctcc taggcttctt ctcacttctc 360 tcttccccaa gcatccttcc tgctgctcgc gcccattcct ccccccacgc cgccccccgc 420 ccggccccca ctcttccgcg cctaggagga cctcctcagg ggaccagatt tccgcgcggc 480 tgcgacccca agcctggcaa catgtggaac gcgacgccca gcgaggagcc ggagcctaac 540 gtcacgctgg acctggactg ggacgcttct cccggcaacg actcactctc tgacgaactg 600 ctgccactgt tccccgcgcc gctgctggcg ggcgtcactg ccacctgcgt ggcgctcttc 660 gtggtgggca tctcgggcaa cctgctcacc atgctggtgg tgtcccgctt ccgcgagctg 720 cgcaccacca ccaacctcta cctatccagc atggccttct ccgatctgct catcttcctg 780 tgcatgccgc tggacctcgt ccgcctctgg cagtatcggc cctggaactt cggcgacctg 840 ctctgcaaac tcttccagtt tgtcagcgag agctgcacct acgccacggt cctcaccatc 900 accgcgctga gcgtcgagcg ctacttcgcc atctgcttcc cgctgcgggc caaggtggtg 960 gtcaccaagg gccgtgtgaa gctggtcatc cttgtcatct gggccgtggc cttctgcagc 1020 gcggggccca tcttcgtgct ggtgggcgtg gagcacgaga acggcacaga tccccgggac 1080 accaacgagt gccgcgccac cgagttcgct gtgcgctctg ggctgctcac cgtcatggtg 1140 tgggtgtcca gcgtcttctt ctttctaccg gtcttctgcc tcactgtgct ctacagtctc 1200 atcgggagga agctatggcg gagacgcggc gatgcagcgg tgggcgcctc gctccgggac 1260 cagaaccaca aacagacagt gaagatgctt ggtgagttct gacaccccgg tggcttttct 1320 tcccccactg cttgctcttt gccagagccc tctatttctg tttctggtcg tctccatctc 1380 tccctaagtc tctcaagtct ctgtctgtct ctgyctctct sttggttctt ggtctcactg 1440 ctttckggtt ttttttcctc tgtctgtccc tgtatcttct ccacgaaaaa gcccctcata 1500 ttggcaattc cctaaatgag tactggtctg ggaaatttgg tccaagatgg aaatacctca 1560 ttatggttta ttgagtcccc taattgttaa yggtkymkcw ymtwgwctca catagaattt 1620 gtggttatcm aagtmataat attaaggtaa gcaggcaggy awtgggttta gaaatyrctc 1680 catggtaart ctaaccamaa awttgggtca ctctgttaar gaygryttat agatgtrttt 1740 tgtttgtttk caatattrgg atttrttytc tgccctgcmy ctkyctcaga taattacatc 1800 cactcttgtt tagtctatgg ttttgccagg aggggcttca tgctggggtc tcctttttct 1860 tgtttttgta tttgtctccc cagtaatata ggccaggata gggtggagaa gtcatccttt 1920 cctcaaactg tccttcagga aggtctgggt actgaacggt tactgcataa actctgcttc 1980 cccaaaggca tgtgcttggt gtggtaaagt catgaagatg gtgctcatgt ccaagaggaa 2040 cctctgatct cacttttcaa gggatttcat gtttgctgac atttaatact tgttagtttt 2100 tgcaggggga tgatttctca tttgcaattt tattattctc aaattctgca tgtcagaatg 2160 ttagagattt ctcagggatg tcaggttctg tttccagatg agtgattgcc ctgtgtcctc 2220 cattggactg taaactcata tgcaccagac agggtctaca ttgctgccgt ggtgcatagc 2280 cttccatgtg tcacttagtc ctaaagagaa gttactaata acctaatctc actaatctca 2340 ctggcatctc aatgccgatc ccattgtcat ctgaaaattt gaaggggaca ttaaagtggc 2400 acagggacca gaacaatatt tttctctcat tgctgaattt taaaaacaat ctaaaaaatt 2460 ggaattcttg aagaaactat cttatatgac taaaatgaag ccttgggtgg gtgctaatta 2520 ttattgtctg gcttacctgc cccccccact acttatatct tttagagatg acacagactt 2580 gctttccctg tggctactaa tcccaattgc acattcagtc ccttgataga cttactctaa 2640 aaatctaagt tcagcggtcc acgaaacata acaaagcctg tcctaaaaca gaaagaaaga 2700 aagaaagaaa gaaagaaaga aagaaagaaa gaaagaaaga aagaaaacag aagacaaaca 2760 aggtctttcc ccattcccta acatacagga atggaaatta ttaagtctac gtgatagcca 2820 atgaatctgt ttcttaagta tgcccacaag ggtgctgccg gagccattgc tcagggctgg 2880 agtatttact gggcatgctt gaccccagca tggagggtga gaagtgctcc tgggaactct 2940 gatccactgc tgtggtggag agcaaacacc tggcctcatt tatacttgtt gtctgtataa 3000 tgcatataaa tggaggataa tcattaatga actgtttagt tgggtcatca tgccaagtca 3060 gtcacaaagc caagtcgtta tcacatagaa agactgggaa gcccagtgga gattgttagc 3120 tgttggtctg acagtctcac tgtgtgctat ctatagtgtt agaacggatg gaggcagtat 3180 ttatgtgaag agcagggtgt cgtgtttcct gtgtcaaaga gcaagatgtg atgtttgtca 3240 gtgggcatgc ccctcatgga gaaaagagat ccgggactta aaaatgtgaa gtgatttatg 3300 ccgtgtcaca cccatgctcc accctgatgg tctctctttg tgtgccttca gctgtggtgg 3360 tgtttgcttt catcctctgc tggctgccct tccacgtggg aagatatctg ttttccaagt 3420 ctttcgagcc tggctctctg gagatcgcgc agatcagtca gtactgcaac ctggtgtcct 3480 ttgtcctctt ctacctcagc gctgccatca accccattct gtacaacatc atgtccaaga 3540 agtaccgggt ggccgtgttc aaacttctag gatttgaatc cttctcccag agaaagcttt 3600 ccactctgaa ggatgagagt tcccgggcct ggacaaagtc gagcatcaat acatgacatc 3660 gcagcgcatc tctccgtcat cgctcattgc tccacaccag aagccatagc caagcgggac 3720 ttgggaggag gcagaacgtc agtttgggga ttagagacaa atggatctgg aaacaattgg 3780 gggtggggag tagagccaga tgggcagggt ccgtgcagat tgatctattt gtgcgcccac 3840 cagagcactc atgtgcagcc cctgcacacc tgtgtctgtg attttgcgaa tttgcatttg 3900 gagcttctga cagctttgca gctcgaagga gggaggggcg cagagcaggc aacggccgtc 3960 cttcttggtg tgtaacacta aactccattt gcttttctca tcataatag 4009 2 1095 DNA Mus musculus 2 atgtggaacg cgacgcccag cgaggagccg gagcctaacg tcacgctgga cctggactgg 60 gacgcttctc ccggcaacga ctcactctct gacgaactgc tgccactgtt ccccgcgccg 120 ctgctggcgg gcgtcactgc cacctgcgtg gcgctcttcg tggtgggcat ctcgggcaac 180 ctgctcacca tgctggtggt gtcccgcttc cgcgagctgc gcaccaccac caacctctac 240 ctatccagca tggccttctc cgatctgctc atcttcctgt gcatgccgct ggacctcgtc 300 cgcctctggc agtatcggcc ctggaacttc ggcgacctgc tctgcaaact cttccagttt 360 gtcagcgaga gctgcaccta cgccacggtc ctcaccatca ccgcgctgag cgtcgagcgc 420 tacttcgcca tctgcttccc gctgcgggcc aaggtggtgg tcaccaaggg ccgtgtgaag 480 ctggtcatcc ttgtcatctg ggccgtggcc ttctgcagcg cggggcccat cttcgtgctg 540 gtgggcgtgg agcacgagaa cggcacagat ccccgggaca ccaacgagtg ccgcgccacc 600 gagttcgctg tgcgctctgg gctgctcacc gtgatggtat gggtgtcgag cgtcttcttc 660 tttctgccgg tcttctgcct cactgtgctc tacagtctca tcgggaggaa gctgtggcgg 720 aggcgcggcg acgcggcggt gggctcctcg ctcagggacc agaaccacaa acagacagtg 780 aagatgcttg ctgtggtggt gtttgctttc atcctctgct ggctgccctt ccacgtggga 840 agatatctgt tttccaagtc tttcgagcct ggctctctgg agatcgcgca gatcagtcag 900 tactgcaacc tggtgtcctt tgtcctcttc tacctcagcg ctgccatcaa ccccattctc 960 tacaacatca tgtccaagaa gtaccgggtg gccgtgttca aacttctagg atttgaatcc 1020 ttctcccaga gaaagctttc cactctgaag gatgagagtt cccgggcctg gacaaagtcg 1080 agcatcaata catga 1095 3 364 PRT Mus musculus 3 Met Trp Asn Ala Thr Pro Ser Glu Glu Pro Glu Pro Asn Val Thr Leu 1 5 10 15 Asp Leu Asp Trp Asp Ala Ser Pro Gly Asn Asp Ser Leu Ser Asp Glu 20 25 30 Leu Leu Pro Leu Phe Pro Ala Pro Leu Leu Ala Gly Val Thr Ala Thr 35 40 45 Cys Val Ala Leu Phe Val Val Gly Ile Ser Gly Asn Leu Leu Thr Met 50 55 60 Leu Val Val Ser Arg Phe Arg Glu Leu Arg Thr Thr Thr Asn Leu Tyr 65 70 75 80 Leu Ser Ser Met Ala Phe Ser Asp Leu Leu Ile Phe Leu Cys Met Pro 85 90 95 Leu Asp Leu Val Arg Leu Trp Gln Tyr Arg Pro Trp Asn Phe Gly Asp 100 105 110 Leu Leu Cys Lys Leu Phe Gln Phe Val Ser Glu Ser Cys Thr Tyr Ala 115 120 125 Thr Val Leu Thr Ile Thr Ala Leu Ser Val Glu Arg Tyr Phe Ala Ile 130 135 140 Cys Phe Pro Leu Arg Ala Lys Val Val Val Thr Lys Gly Arg Val Lys 145 150 155 160 Leu Val Ile Leu Val Ile Trp Ala Val Ala Phe Cys Ser Ala Gly Pro 165 170 175 Ile Phe Val Leu Val Gly Val Glu His Glu Asn Gly Thr Asp Pro Arg 180 185 190 Asp Thr Asn Glu Cys Arg Ala Thr Glu Phe Ala Val Arg Ser Gly Leu 195 200 205 Leu Thr Val Met Val Trp Val Ser Ser Val Phe Phe Phe Leu Pro Val 210 215 220 Phe Cys Leu Thr Val Leu Tyr Ser Leu Ile Gly Arg Lys Leu Trp Arg 225 230 235 240 Arg Arg Gly Asp Ala Ala Val Gly Ser Ser Leu Arg Asp Gln Asn His 245 250 255 Lys Gln Thr Val Lys Met Leu Ala Val Val Val Phe Ala Phe Ile Leu 260 265 270 Cys Trp Leu Pro Phe His Val Gly Arg Tyr Leu Phe Ser Lys Ser Phe 275 280 285 Glu Pro Gly Ser Leu Glu Ile Ala Gln Ile Ser Gln Tyr Cys Asn Leu 290 295 300 Val Ser Phe Val Leu Phe Tyr Leu Ser Ala Ala Ile Asn Pro Ile Leu 305 310 315 320 Tyr Asn Ile Met Ser Lys Lys Tyr Arg Val Ala Val Phe Lys Leu Leu 325 330 335 Gly Phe Glu Ser Phe Ser Gln Arg Lys Leu Ser Thr Leu Lys Asp Glu 340 345 350 Ser Ser Arg Ala Trp Thr Lys Ser Ser Ile Asn Thr 355 360 4 366 PRT Homo sapiens 4 Met Trp Asn Ala Thr Pro Ser Glu Glu Pro Gly Phe Asn Leu Thr Leu 1 5 10 15 Ala Asp Leu Asp Trp Asp Ala Ser Pro Gly Asn Asp Ser Leu Gly Asp 20 25 30 Glu Leu Leu Gln Leu Phe Pro Ala Pro Leu Leu Ala Gly Val Thr Ala 35 40 45 Thr Cys Val Ala Leu Phe Val Val Gly Ile Ala Gly Asn Leu Leu Thr 50 55 60 Met Leu Val Val Ser Arg Phe Arg Glu Leu Arg Thr Thr Thr Asn Leu 65 70 75 80 Tyr Leu Ser Ser Met Ala Phe Ser Asp Leu Leu Ile Phe Leu Cys Met 85 90 95 Pro Leu Asp Leu Val Arg Leu Trp Gln Tyr Arg Pro Trp Asn Phe Gly 100 105 110 Asp Leu Leu Cys Lys Leu Phe Gln Phe Val Ser Glu Ser Cys Thr Tyr 115 120 125 Ala Thr Val Leu Thr Ile Thr Ala Leu Ser Val Glu Arg Tyr Phe Ala 130 135 140 Ile Cys Phe Pro Leu Arg Ala Lys Val Val Val Thr Lys Gly Arg Val 145 150 155 160 Lys Leu Val Ile Phe Val Ile Trp Ala Val Ala Phe Cys Ser Ala Gly 165 170 175 Pro Ile Phe Val Leu Val Gly Val Glu His Glu Asn Gly Thr Asp Pro 180 185 190 Trp Asp Thr Asn Glu Cys Arg Pro Thr Glu Phe Ala Val Arg Ser Gly 195 200 205 Leu Leu Thr Val Met Val Trp Val Ser Ser Ile Phe Phe Phe Leu Pro 210 215 220 Val Phe Cys Leu Thr Val Leu Tyr Ser Leu Ile Gly Arg Lys Leu Trp 225 230 235 240 Arg Arg Arg Arg Gly Asp Ala Val Val Gly Ala Ser Leu Arg Asp Gln 245 250 255 Asn His Lys Gln Thr Val Lys Met Leu Ala Val Val Val Phe Ala Phe 260 265 270 Ile Leu Cys Trp Leu Pro Phe His Val Gly Arg Tyr Leu Phe Ser Lys 275 280 285 Ser Phe Glu Pro Gly Ser Leu Glu Ile Ala Gln Ile Ser Gln Tyr Cys 290 295 300 Asn Leu Val Ser Phe Val Leu Phe Tyr Leu Ser Ala Ala Ile Asn Pro 305 310 315 320 Ile Leu Tyr Asn Ile Met Ser Lys Lys Tyr Arg Val Ala Val Phe Arg 325 330 335 Leu Leu Gly Phe Glu Pro Phe Ser Gln Arg Lys Leu Ser Thr Leu Lys 340 345 350 Asp Glu Ser Ser Arg Ala Trp Thr Glu Ser Ser Ile Asn Thr 355 360 365 5 364 PRT Rattus norvegicus 5 Met Trp Asn Ala Thr Pro Ser Glu Glu Pro Glu Pro Asn Val Thr Leu 1 5 10 15 Asp Leu Asp Trp Asp Ala Ser Pro Gly Asn Asp Ser Leu Pro Asp Glu 20 25 30 Leu Leu Pro Leu Phe Pro Ala Pro Leu Leu Ala Gly Val Thr Ala Thr 35 40 45 Cys Val Ala Leu Phe Val Val Gly Ile Ser Gly Asn Leu Leu Thr Met 50 55 60 Leu Val Val Ser Arg Phe Arg Glu Leu Arg Thr Thr Thr Asn Leu Tyr 65 70 75 80 Leu Ser Ser Met Ala Phe Ser Asp Leu Leu Ile Phe Leu Cys Met Pro 85 90 95 Leu Asp Leu Val Arg Leu Trp Gln Tyr Arg Pro Trp Asn Phe Gly Asp 100 105 110 Leu Leu Cys Lys Leu Phe Gln Phe Val Ser Glu Ser Cys Thr Tyr Ala 115 120 125 Thr Val Leu Thr Ile Thr Ala Leu Ser Val Glu Arg Tyr Phe Ala Ile 130 135 140 Cys Phe Pro Leu Arg Ala Lys Val Val Val Thr Lys Gly Arg Val Lys 145 150 155 160 Leu Val Ile Leu Val Ile Trp Ala Val Ala Phe Cys Ser Ala Gly Pro 165 170 175 Ile Phe Val Leu Val Gly Val Glu His Glu Asn Gly Thr Asp Pro Arg 180 185 190 Asp Thr Asn Glu Cys Arg Ala Thr Glu Phe Ala Val Arg Ser Gly Leu 195 200 205 Leu Thr Val Met Val Trp Val Ser Ser Val Phe Phe Phe Leu Pro Val 210 215 220 Phe Cys Leu Thr Val Leu Tyr Ser Leu Ile Gly Arg Lys Leu Trp Arg 225 230 235 240 Arg Arg Gly Asp Ala Ala Val Gly Ala Ser Leu Arg Asp Gln Asn His 245 250 255 Lys Gln Thr Val Lys Met Leu Ala Val Val Val Phe Ala Phe Ile Leu 260 265 270 Cys Trp Leu Pro Phe His Val Gly Arg Tyr Leu Phe Ser Lys Ser Phe 275 280 285 Glu Pro Gly Ser Leu Glu Ile Ala Gln Ile Ser Gln Tyr Cys Asn Leu 290 295 300 Val Ser Phe Val Leu Phe Tyr Leu Ser Ala Ala Ile Asn Pro Ile Leu 305 310 315 320 Tyr Asn Ile Met Ser Lys Lys Tyr Arg Val Ala Val Phe Lys Leu Leu 325 330 335 Gly Phe Glu Ser Phe Ser Gln Arg Lys Leu Ser Thr Leu Lys Asp Glu 340 345 350 Ser Ser Arg Ala Trp Thr Lys Ser Ser Ile Asn Thr 355 360 6 366 PRT Sus scrofa 6 Met Trp Asn Ala Thr Pro Ser Glu Glu Pro Gly Pro Asn Leu Thr Leu 1 5 10 15 Pro Asp Leu Gly Trp Asp Ala Pro Pro Glu Asn Asp Ser Leu Val Glu 20 25 30 Glu Leu Leu Pro Leu Phe Pro Thr Pro Leu Leu Ala Gly Val Thr Ala 35 40 45 Thr Cys Val Ala Leu Phe Val Val Gly Ile Ala Gly Asn Leu Leu Thr 50 55 60 Met Leu Val Val Ser Arg Phe Arg Glu Met Arg Thr Thr Thr Asn Leu 65 70 75 80 Tyr Leu Ser Ser Met Ala Phe Ser Asp Leu Leu Ile Phe Leu Cys Met 85 90 95 Pro Leu Asp Leu Phe Arg Leu Trp Gln Tyr Arg Pro Trp Asn Leu Gly 100 105 110 Asn Leu Leu Cys Lys Leu Phe Gln Phe Val Ser Glu Ser Cys Thr Tyr 115 120 125 Ala Thr Val Leu Thr Ile Thr Ala Leu Ser Val Glu Arg Tyr Phe Ala 130 135 140 Ile Cys Phe Pro Leu Arg Ala Lys Val Val Val Thr Lys Gly Arg Val 145 150 155 160 Lys Leu Val Ile Leu Val Ile Trp Ala Val Ala Phe Cys Ser Ala Gly 165 170 175 Pro Ile Phe Val Leu Val Gly Val Glu His Asp Asn Gly Thr Asp Pro 180 185 190 Arg Asp Thr Asn Glu Cys Arg Ala Thr Glu Phe Ala Val Arg Ser Gly 195 200 205 Leu Leu Thr Val Met Val Trp Val Ser Ser Val Phe Phe Phe Leu Pro 210 215 220 Val Phe Cys Leu Thr Val Leu Tyr Ser Leu Ile Gly Arg Lys Leu Trp 225 230 235 240 Arg Arg Lys Arg Gly Glu Ala Ala Val Gly Ser Ser Leu Arg Asp Gln 245 250 255 Asn His Lys Gln Thr Val Lys Met Leu Ala Val Val Val Phe Ala Phe 260 265 270 Ile Leu Cys Trp Leu Pro Phe His Val Gly Arg Tyr Leu Phe Ser Lys 275 280 285 Ser Leu Glu Pro Gly Ser Val Glu Ile Ala Gln Ile Ser Gln Tyr Cys 290 295 300 Asn Leu Val Ser Phe Val Leu Phe Tyr Leu Ser Ala Ala Ile Asn Pro 305 310 315 320 Ile Leu Tyr Asn Ile Met Ser Lys Lys Tyr Arg Val Ala Val Phe Lys 325 330 335 Leu Leu Gly Phe Glu Pro Phe Ser Gln Arg Lys Leu Ser Thr Leu Lys 340 345 350 Asp Glu Ser Ser Arg Ala Trp Thr Glu Ser Ser Ile Asn Thr 355 360 365 7 39 DNA PCR primer 7 gggcccgaat tcgccgccat gtggaacgcg acgcccagc 39 8 30 DNA PCR primer 8 caccaccaca gcaagcatct tcactgtctg 30 9 33 DNA PCR primer 9 aagatgcttg ctgtggtggt gtttgctttc atc 33 10 38 DNA PCR primer 10 agtttagcgg ccgctcatgt attgatgctc gactttgt 38 

What is claimed is:
 1. An isolated mouse growth hormone secretagogue receptor (mGHS-R) comprising the amino acid sequence set forth in SEQ ID NO:3.
 2. The mGHS-R according to claim 1 wherein said receptor is activated by a growth hormone secretagogue selected from the group consisting of releasing peptide GHRP-6 or MK-0677.
 3. An isolated nucleic acid molecule comprising the nucleotide sequence set forth in SEQ ID NO:1.
 4. The nucleic acid according to claim 3 which is DNA.
 5. An isolated nucleic acid which encodes a mouse growth hormone secretagogue receptor comprising the amino acid sequence set forth in SEQ ID NO:3.
 6. A vector comprising the isolated nucleic acid molecule according to claim
 5. 7. A vector according to claim 6 which is selected from the group consisting of: plasmids, modified viruses, yeast artificial chromosomes, bacteriophages, cosmids and transposable elements.
 8. A host cell comprising the vector according to claim
 6. 9. A method of identifying ligands which comprises: (a) contacting the mGHS-R according to claim 2 with compounds suspected of being mGHS-R ligands; and (b) determining whether binding occurs, binding constituting a positive indication of the presence of a ligand.
 10. An isolated nucleic acid molecule consisting of the nucleotide sequence set forth in SEQ ID NO:2 wherein said nucleotide sequence encodes a mGHS-R.
 11. A vector comprising the nucleic acid molecule according to claim
 10. 12. A host cell comprising the vector according to claim
 11. 